[voraa]

var arr1 = [
{'a':1,'b':2},
{'a':3,'b':4}
]
 
var arr2 = [
{'c':1,'d':5},
{'c':4,'d':4}
 
]

const b = arr1.find (a1 => arr2.every (a2 => a2.c != a1.a))?.b;
console.log (b);